Electromagnetic radiation such as light can be collected and condensed using imaging or non-imaging systems. An imaging system produces an image of an arc at a certain location in an optical path. A non-imaging system does not produce an image of an arc, but delivers an optical beam with a certain area, aspect ratio and cone angle.
A common method for light collection is based on a system using a parabolic or ellipsoid reflector of the imaging or non-imaging type. FIG. 1A shows a prior art lamp/reflector system 10 in which a lamp 12 is placed at a first focus of an ellipsoid reflector 11. The ellipsoid reflector 11 focuses the light beam 13 into a second focus 14 located on the optical axis 5. A target (not shown) is usually placed at this second focus 14.
FIG. 1B shows another prior art lamp/reflector system 20 in which a lamp 22 is placed at a focus of a parabolic reflector 21. The parabolic reflector 21 delivers a collimated light beam 23 parallel to an optical axis 15. A focusing lens (not shown) can be used to collect the collimated beam 23 and focus it into a target (not shown) located somewhere on the optical axis 15.
Both systems shown in FIGS. 1A-1B are on-axis systems, since the components are aligned along an optical axis. Systems based on off-axis configurations are also known. For example, U.S. Pat. Nos. 5,414,600 and 5,430,634 describe off-axis collection systems of the imaging type. Non-imaging collection systems are discussed, for example, in U.S. Pat. No. 5,271,077 to Brockman, Kacia et al. and U.S. Pat. No. 6,554,456 to Buelow et al.
Non-imaging light collection systems have been described in U.S. Pat. No. 5,773,918 to Dolan et al. and U.S. Pat. No. 6,509,675 to MacLennan et al. In such systems, a reflective coating is applied directly to the bulb surface of an electrodeless lamp (and sometimes a reflective jacket surrounds the bulb) leaving a port open in the reflective coating (or the reflective jacket) to form an aperture. Light exits the collection system through the aperture and can be collimated via known imaging or non-imaging optics to obtain the desired cone angle. These collection systems do not provide a way to control the spatial distribution of light in terms of angle and intensity at each point across the aperture. In addition, the Dolan and MacLennan patents focus on electrodeless lamps and do not provide effective means to apply such collection schemes to electroded lamps.
Many known electromagnetic radiation collection systems suffer from the following problems. First, many of these systems are relatively large, making them less attractive for many applications such as portable projection display systems. Second, these systems provide limited control over the spatial distribution of delivered light in terms of intensity and angle. Third, due to the large optical aberrations typical of these reflector types, etendue (angular extent) of the light beam is not preserved in most cases, leading to radiation losses at the target. Finally, many of these systems collect only part of the light emitted from a source. Specifically, they collect those light rays that strike the reflector after being emitted from the source. Light rays that do not strike the reflector typically do not get collected, and are thus wasted.
Therefore, there is a need for compact, lightweight, and efficient light collection system that provides control over spatial distribution of light in terms of intensity and angle over a certain target area, such as the active area of a display panel.